AI agents call ha_list_devices to retrieve information from Hass without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and lists device information from Home Assistant's device registry. It performs a read-only query operation that returns data without creating, modifying, deleting, or executing any actions. The blast radius of misuse is minimal—an agent could only enumerate devices but cannot control them or access sensitive data beyond device names/identifiers.
From the tool's definition Tool name 'ha_list_devices' and description 'List Home Assistant devices from the device registry' indicate a query/retrieval operation with no modification or side effects.
Attacks that exploit this kind of access
List Home Assistant devices from the device registry. It is categorised as a Read tool in the Hass MCP Server, which means it retrieves data without modifying state.
Register the Hass MCP server in PolicyLayer and add a rule for ha_list_devices: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Hass. Nothing to install.
ha_list_devices is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the ha_list_devices rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for ha_list_devices. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
ha_list_devices is provided by the Hass MCP server (thewhykiki/hass-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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